This invention relates to a glass-encapsulated semiconductor device and more particularly to a glass-encapsulated semiconductor device in which the same encapsulating glass can be used independent of the number of the laminated semiconductor pellets.
The glass-encapsulated semiconductor device in which semiconductor pellets are laminated and bonded together and to a pair of electrodes, in which the exposed edges of the pn junctions of the semiconductor pellets are surface-passivated and in which an encapsulating sintered glass layer is coated for hermetically sealing the pellets on the laminated pellets over the length from one electrode to the other, has a fatal problem that the encapsulating glass layer or the semiconductor pellets are sometimes broken in the process of fabrication or during use.
The breakage of the glass layer or the pellets is caused by thermal stress generated due to the difference in thermal expansion among different members.
In the case where only one or two pellets are used, the effect of soldering material layers, the total thickness of which is rather small, upon the average thermal expansion coefficient of the laminated pellets can be neglected even when the thermal expansion coefficient of the soldering material is greater than that of the semiconductor pellet. Accordingly, the thermal expansion coefficient of the encapsulating glass can be approximated to that of silicon.
On the other hand, in the case where the number of the laminated pellets is as large as thirty or so, the total thickness of the soldering material layers cannot be neglected so that there is a need for selecting in such a case an encapsulating glass having a thermal expansion coefficient approximating to the average thermal expansion coefficient of the laminated column of semiconductor pellets and soldering material layers.
This means that the quality of the encapsulating glass should be selected depending upon the number of the laminated pellets.
It is very difficult to select a suitable glass for encapsulating semiconductor pellets, having an appropriate thermal expansion coefficient without degrading its function of surface passivation.
In U.S. Pat. No. 3,913,127, in case where the number of the laminated pellets is large, it has been proposed to approximate the average thermal expansion coefficient of the laminated column of semiconductor pellets to the encapsulating glass by varying the respective thicknesses of the pellets and soldering material or inserting spacers. However, it was not necessary to change the material of the glass but necessary to adjust the respective thickness of the semiconductor pellets, soldering material and spacers.